1. Field of the Invention
The present invention relates to a method of impregnating resin in a frictional plate such as a brake pad, a clutch facing usable for transmitting the driving torque generated by an engine to driving wheels for a vehicle.
2. Description of the Related Art
A frictional plate usable for the purpose of power transmission is built in a friction brake or clutch for a vehicle in order to transmit the power generated by an engine to driving wheels by utilizing the frictional resistance appearing when the surface of each frictional plate is thrusted against a rotational plate facing thereto. In view of the foregoing fact, it has been required that the frictional plate exhibits a large magnitude of frictional resistance, sufficiently proofs against the heat generated by friction, and hardly wears. The frictional plate which can satisfactorily meet the foregoing requirement is typically exemplified by a frictional plate which is constructed such that a paper-shaped fiber based substrate including inorganic filler as friction increasing material therein is joined to a metallic base plate, it is impregnated with a predetermined quantity of thermosetting resin having excellent heat resistance as a bonding agent, and subsequently, it is heated and cured, whereby not only a mechanical strength but also thermal conductivity of the frictional plate are substantially increased.
The hitherto known conventional resin impregnating method applicable to the power transmitting frictional plate constructed in the above-described manner is practiced such that a frictional plate impregnated with no resin is dipped in a resin bath, it is subjected to resin impregnating treatment for a predetermined time in a normal pressure atmosphere or a reduced pressure atmosphere, subsequently, an extra quantity of resin is drained or removed from the frictional plate for a long time in the environmental atmosphere or it is forcibly wiped off from the frictional plate by thrusting a roller against the latter, and thereafter, the resin impregnated in the frictional plate is cured at a room temperature or it is subjected to curing treatment by blowing hot air to the frictional plate.
When this conventional resin impregnating method is employed, a number of frictional plates can be handled at the same time but there is liable to arise a malfunction that the frictional plate is irregularly impregnated with the resin, the resin quickly flows out of the frictional plate during resin draining treatment or drop-like resin spots appear on the frictional plate. For this reason, with the conventional resin impregnating method, there often arises a difficulty that a predetermined quantity of resin is uniformly impregnated in the fiber based substrate. This leads to the problem that properties of the thus obtained frictional plate are liable to fluctuate. In addition, with the conventional resin impregnating method, since the resin adheres to the whole surface of the frictional plate, many manhours are required for masking a plurality of threaded holes formed in or through a metallic base plate with a certain sheet-like material, and moreover, wiping an extra quantity of resin from the fiber based substrate with an operator's hand. Consequently, the conventional resin impregnating method has drawbacks that each frictional plate is treated or worked for a long time at an increased cost, and an increased quantity of resin is consumed during the impregnating treatment.
In addition, with the conventional resin impregnating method, since a number of frictional plates are subjected to impregnating treatment at the same time, a large quantity of resin is required for achieving impregnating treatment for producing the frictional plates. Additionally, since it is required that a measure is taken for protecting a building and associated facilities from possible explosion caused attributable to inflammable volatile solvent contained in a large quantity of resin, an installation cost required for practicing the conventional impregnating method is undesirably increased. When the resin accumulatively received in a resin bath is contaminated with foreign material adhering to the frictional plate, it is required that the contaminated resin is cleaned by removing the foreign material therefrom. Further, since a concentration and viscosity of each of non-volatile components of the resin are increased due to chemical transformation of the resin caused by the evaporation of the solvent from the resin and the absorption of environmental moisture in the latter, it is practically difficult to keep the viscosity of the resin in the resin bath constant, resulting in a high controlling cost being required for practicing the resin impregnating method. Once the resin in the resin bath is contaminated with foreign material, there arises a problem that the viscosity of the resin varies, causing a quality of product, i.e., frictional plate to be adversely affected by the varied viscosity.
Moreover, with the conventional resin impregnating method, when a number of frictional plates are subjected to impregnating treatment at the same time, a large volume of solvent vapor is generated from the frictional plates not only during the resin draining step but also during the resin drying step, resulting in the concentration of organic solvent in the working environment being increased. To cope with the foregoing malfunction, it is necessary that a large-sized ventilating unit is installed in operative association with a resin impregnating apparatus in order to prevent the concentration of organic solvent in the working environment from being increased. At this time, however, there arises another problems that noisy sound is generated due to the large-sized ventilating unit installed in that way, and moreover, the working environment is contaminated with the resin which falls down from the frictional plates. In the circumstances as mentioned above, many requests have been raised from users for satisfactorily solving various problems as mentioned above.